838 research outputs found

    Serendipitously Detected Galaxies in the Hubble Deep Field

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    We present a catalog of 74 galaxies detected serendipitously during a campaign of spectroscopic observations of the Hubble Deep Field North (HDF) and its environs. Among the identified objects are five candidate Ly-alpha emitters at z > 5, a galaxy cluster at z = 0.85, and a Chandra source with a heretofore undetermined redshift of z = 2.011. We report redshifts for 25 galaxies in the central HDF, 13 of which had no prior published spectroscopic redshift. Of the remaining 49 galaxies, 30 are located in the single-orbit HDF Flanking Fields. We discuss the redshift distribution of the serendipitous sample, which contains galaxies in the range 0.10 < z < 5.77 with a median redshift of z = 0.85, and we present strong evidence for redshift clustering. By comparing our spectroscopic redshifts to optical/IR photometric studies of the HDF, we find that photometric redshifts are in most cases capable of producing reasonable predictions of galaxy redshifts. Finally, we estimate the line-of-sight velocity dispersion and the corresponding mass and expected X-ray luminosity of the galaxy cluster, we present strong arguments for interpreting the Chandra source as an obscured AGN, and we discuss in detail the spectrum of one of the candidate z > 5 Ly-alpha emitters.Comment: 18 pages, 9 figures, accepted for publication in the Astronomical Journa

    Optical Morphology Evolution of Infrared Luminous Galaxies in GOODS-N

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    We combine optical morphologies and photometry from HST, redshifts from Keck, and mid-infrared luminosities from Spitzer for an optically selected sample of~800 galaxies in GOODS-N to track morphology evolution of infrared luminous galaxies (LIRGs) since redshift z=1. We find a 50% decline in the number of LIRGs from z~1 to lower redshift, in agreement with previous studies. In addition, there is evidence for a morphological evolution of the populations of LIRGs. Above z=0.5, roughly half of all LIRGs are spiral, the peculiar/irregular to spiral ratio is ~0.7, and both classes span a similar range of L_{IR} and M_B. At low-z, spirals account for one-third of LIRGs, the peculiar to spiral fraction rises to 1.3, and for a given M_B spirals tend to have lower IR luminosity than peculiars. Only a few percent of LIRGs at any redshift are red early-type galaxies. For blue galaxies (U-B < 0.2), M_B is well correlated with log(L_{IR}) with an RMS scatter (about a bivariate linear fit) of ~0.25 dex in IR luminosity. Among blue galaxies that are brighter than M_B = -21, 75% are LIRGs, regardless of redshift. These results can be explained by a scenario in which at high-z, most large spirals experience an elevated star formation rate as LIRGs. Gas consumption results in a decline of LIRGs, especially in spirals, to lower redshifts.Comment: 6 pages, 2 figures, accepted ApJ

    Dusty Starbursts and the Growth of Cosmic Structure

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    Dusty starbursts were more numerous around z~1 than today and appear to be responsible for the majority of cosmic star formation over the Hubble time. We suggest that they represent a common phase within galaxies in general which is triggered by the growth of cosmic structure. We discuss the origin of the luminosity of luminous infrared galaxies at z~1. Are these galaxies dominated by star formation or nuclear activity ? What is triggering their strong activity ? Is it triggered by external interactions or did it happen naturally within isolated galaxies ? We present HST-ACS high resolution optical images of luminous infrared galaxies at z~0.7 showing the evolution of the morphology of these galaxies as a function of infrared luminosity, or star formation rate, and discuss the effect of the environment on their activity.Comment: 4 pages, 2 figures, to appear in Proceeding of the "Multi-Wavelength Cosmology" Conference held in Mykonos, Greece, June 2003, ed.M. Plionis (Kluwer

    NIR Spectroscopy with the VLT of a sample of ISO selected Hubble Deep Field South Galaxies

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    A new population of faint galaxies characterized by an extremely high rate of evolution with redshift up to z~1.5 has recently been discovered by ISO. These sources are likely to contribute significantly to the cosmic far-IR extragalactic background. We have carried out near-infrared VLT-ISAAC spectroscopy of a sample of ISOCAM galaxies from the Hubble Deep Field South. The rest-frame R-band spectral properties of the ISO population resembles that of powerful dust-enshrouded active starburst galaxies.Comment: 8 pages, 3 figures, to appear in "ISO Surveys of a Dusty Universe", eds. D. Lemke, M. Stickel, K. Wilke, typos correcte

    NGC6240: extended CO structures and their association with shocked gas

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    We present deep CO observations of NGC6240 performed with the IRAM Plateau de Bure Interferometer (PdBI). NGC6240 is the prototypical example of a major galaxy merger in progress, caught at an early stage, with an extended, strongly-disturbed butterfly-like morphology and the presence of a heavily obscured active nucleus in the core of each progenitor galaxy. The CO line shows a skewed profile with very broad and asymmetric wings detected out to velocities of -600 km/s and +800 km/s with respect to the systemic velocity. The PdBI maps reveal the existence of two prominent structures of blueshifted CO emission. One extends eastward, i.e. approximately perpendicular to the line connecting the galactic nuclei, over scales of ~7 kpc and shows velocities up to -400 km/s. The other extends southwestward out to ~7 kpc from the nuclear region, and has a velocity of -100 km/s with respect to the systemic one. Interestingly, redshifted emission with velocities 400 to 800 km/s is detected around the two nuclei, extending in the east-west direction, and partly overlapping with the eastern blue-shifted structure, although tracing a more compact region of size ~1.7 kpc. The overlap between the southwestern CO blob and the dust lanes seen in HST images, which are interpreted as tidal tails, indicates that the molecular gas is deeply affected by galaxy interactions. The eastern blueshifted CO emission is co-spatial with an Halpha filament that is associated with strong H2 and soft X-ray emission. The analysis of Chandra X-ray data provides strong evidence for shocked gas at the position of the Halpha emission. Its association with outflowing molecular gas supports a scenario where the molecular gas is compressed into a shock wave that propagates eastward from the nuclei. If this is an outflow, the AGN are likely the driving force.Comment: Accepted for publication in A&

    CEA Bolometer Arrays: the First Year in Space

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    The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16 pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics, the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system

    A New Method for ISOCAM Data Reduction - I. Application to the European Large Area ISO Survey Southern Field: Method and Results

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    We have developed a new data reduction technique for ISOCAM LW data and have applied it to the European Large Area ISO Survey (ELAIS) LW3 (15 micron) observations in the southern hemisphere (S1). This method, known as LARI technique and based on the assumption of the existence of two different time scales in ISOCAM transients (accounting either for fast or slow detector response), was particularly designed for the detection of faint sources. In the ELAIS S1 field we obtained a catalogue of 462 15 micron sources with signal-to-noise ratio >= 5 and flux densities in the range 0.45 - 150 mJy (filling the whole flux range between the Deep ISOCAM Surveys and the IRAS Faint Source Survey). The completeness at different flux levels and the photometric accuracy of this catalogue have been tested with simulations. Here we present a detailed description of the method and discuss the results obtained by its application to the S1 LW3 data.Comment: 20 pages, LaTeX, MNRAS style, 20 postscript figures, full catalogue not yet available at http://boas5.bo.astro.it/~elais/catalogues/. Accepted for publication in MNRA

    A Submillimeter and Radio Survey of Gamma-Ray Burst Host Galaxies: A Glimpse into the Future of Star Formation Studies

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    We present the first comprehensive search for submillimeter and radio emission from the host galaxies of twenty well-localized gamma-ray bursts (GRBs). With the exception of a single source, all observations were undertaken months to years after the GRB explosions to ensure negligible contamination from the afterglows. We detect the host galaxy of GRB 000418 in both the sub-mm and radio, and the host galaxy of GRB 000210 only in the sub-mm. These observations, in conjunction with the previous detections of the host galaxies of GRB 980703 and GRB 010222, indicate that about 20% of GRB host galaxies are ultra-luminous and have star formation rates of about 500 M_sun/yr. As an ensemble, the non-detected hosts have a star formation rate of about 100 M_sun/yr (5-sigma) based on their radio emission. The detected and ensemble star formation rates exceed the optical values by an order of magnitude, indicating significant dust obscuration. In the same vein, the ratio of bolometric dust luminosity to UV luminosity for the hosts detected in the sub-mm and radio ranges from 20-800, and follows the known trend of increasing obscuration with increasing bolometric luminosity. We also show that, both as a sample and individually, the GRB host galaxies have bluer R-K colors as compared with galaxies selected in the sub-mm in the same redshift range. This possibly indicates that the stellar populations in the GRB hosts are on average younger, supporting the massive stellar progenitor scenario for GRBs, but it is also possible that GRB hosts are on average less dusty.Comment: Submitted to ApJ; 36 pages, 3 tables, 7 figures; updated reference
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